Defect inspection and charged particle beam apparatus

ABSTRACT

In a defect inspection apparatus which combines a plurality of probes for measuring electric properties of a specimen including a fine circuit line pattern with a charged particle beam apparatus, the charged particle beam apparatus reduces a degradation in resolution even with an image-shift of ±75 μm or more. The defect inspection apparatus has a CAD navigation function associated with an image-shift function. The CAD navigation function uses coordinates for converting an image-shift moving amount to a DUT stage moving amount in communications between an image processing unit for processing charged particle beam images and a memory for storing information on circuit line patterns. The defect inspection provides the user with significantly improved usability.

BACKGROUND OF THE INVENTION

The present invention relates to a charged particle beam apparatus, forexample, an apparatus such as a scanning electron microscope (SEM) forobserving a fine pattern on a semiconductor or a general specimen, and adefect inspection apparatus for measuring electrical properties of anelectronic device using a fine probe, and more particularly, to a fieldof view determining method for bringing a probe into contact with aspecimen using an image-shift function of a charged particle beamapparatus, and a defect inspection apparatus using the field of viewdetermining method.

Conventionally, known inspection apparatuses for detecting electricaldefects in fine electronic circuits formed on semiconductor chipsinclude inspection apparatuses such as an electron beam tester, i.e., EBtester, a probing apparatus, and the like. The EB tester is an apparatuswhich irradiates an electron beam onto a site under measurement, anddetects electrically defective sites of an LSI, taking advantage of thefact that the amount of secondary electrons generated from a site undermeasurement varies depending on a voltage at the site under measurement.The probing apparatus in turn is an apparatus which brings a pluralityof probes or mechanical probes, arranged to match the positions ofproperty measuring pads of an LSI, into contact with measuring pads andplugs to measure the electrical properties of the LSI. With these EBtester and probing apparatus, an operator manually confirms a site withwhich a probe should be brought into contact, while viewing an image ofwires such as an optical microscope (OM) image, a SEM image and thelike.

In recent years, increasingly complicated circuit patterns have beenformed on semiconductor devices such as LSI's, thereby making it moreand more difficult to move a probe to an optimal probing position in ashort time. To overcome the difficulties, a technique called “CADnavigation” displays the wiring layout of a semiconductor device inagreement with an actual image of the semiconductor device, referencedby an operator, during a probing operation to reduce a time required forthe probing operation.

The SEM image is observed using a scanning electron microscope whichscans a primary electron beam on a specimen or semiconductor to capturea scanned image of a fine pattern on the specimen. In order to correctlymove a scan area or field of view of the primary electron beam to apoint under observation on a specimen, an apparatus intended to observea fine pattern on the specimen has an image-shift function whichelectrically deflects the primary electron beam to electrically move aview area in a range of several μm to approximately 10 μm usingdeflectors systems in series.

Also, since the image-shift function directs the primary electron beamobliquely into an objective lens, off-axis aberrations of the objectivelens cause a degradation in the resolution of SEM images. To solve thisproblem, JP-A-10-247465, for example, discloses a technique for removingthe off-axis aberrations as a function of an image-shift amount.Particularly, observations on patterned specimen such as semiconductorsare generally made on the order of sub-nanometers or nanometers usinglow accelerating voltages equal to or lower than 5 kV in order toprevent the specimen from being charged up. When the image-shiftfunction is used for the foregoing purposes under the foregoingconditions, it is necessary to reduce off-axis chromatic aberration andchromatic aberration associated with image-shift deflection.

When the image-shift function is not used, i.e., when the object pointof an objective lens does not move, chromatic aberration of theobjective lens is effectively reduced to improve the resolution by aretarding method which involves applying a negative voltage to aspecimen, or by a boosting method which involves applying a positivevoltage into an objective lens. On the other hand, when a specimen isirradiated with an oblique primary electron beam, i.e., in beam tilting,the primary electron beam is intentionally directed out of the axis ofan objective lens to generate chromatic aberration, and the chromaticaberration is canceled out using an electrostatic and magneticmultipolor, as disclosed, for example, in JP-A-2001-15055.

While the aforementioned image-shift based movements of the field ofview can be substituted by mechanical movements of a DUT stage, theimage-shift function is superior in terms of the moving speed andaccuracy. Even if the specimen stage (DUT) stage is improved in movingaccuracy, mechanical movements cause vibrations at all times. Mechanicalvibrations, if any, could damage probes because several probes are oftensimultaneously brought into contact with measurement plugs during asimultaneous observation in the same SEM field before other probes arebrought into contact.

Thus, the operability of a defect analyzer will be significantlyimproved to reduce a burden on the user if the primary electron beam canbe irradiated to a widest possible area, and if the CAD navigationfunction can be associated with the image-shift function which reduceschromatic aberration.

SUMMARY OF THE INVENTION

In recent years, increasingly complicated circuit patterns have beenformed on semiconductor devices such as LSI's, thereby making it moreand more difficult to move a probe to an optimal probing position in ashort time, and the CAD navigation is effective for quick movements of aprobe to an optimal proving position, as has been described above.However, the current CAD navigation only takes into consideration thedriving of a DUT stage. The image-shift function is essential to preventdamages of probes due to mechanical vibrations of the DUT stage asmentioned above to accomplish high-speed and accurate movements of thefield of view. However, there is no disclosed technique on the CADnavigation linked to the image-shift function.

It is not practically feasible to completely replace a DUT stage drivingrange by the image-shift. However, a need exists for a widest possiblearea irradiated with the primary electron beam. As will be described indetail later in connection with embodiments, for example, consideringfrom a sector width of a current semiconductor memory mat, ±75 μm ormore is required for an image-shift movement amount, while 150 μm ormore is required for a total movement range. Further the size of plugsis required to be equal to or less than 200 nm, and observations shouldbe made at a high resolution of at least 10 k or higher of SEMmagnification.

The apparatus disclosed in JP-A-10-247465 can remove off-axis aberrationdue to a primary electron beam obliquely incident on an objective lensto provide high-resolution SEM images even with an image-shift amountfive times as much as the conventional image-shift amount of several μmto approximately 10 μm. However, it is chromatic aberration due todeflection which is prominent with an image-shift of ±75 μm or more, butJP-A-10-247465 does not take into consideration the deflected chromaticaberration.

Even when the image-shift is used, the chromatic aberration can bereduced by the retarding method or boosting method. However, theretarding method involves applying a specimen with a voltage of −1 kvolts or higher. In a defect inspection apparatus, probes are directlybrought into contact with plugs for electric measurements, so that avoltage applied to a specimen will cause damages of not only the probesand plugs but also an overall device due to a discharge.

The image-shift is similar to the beam tilting, which has been used inrecent years for three-dimensional observations on fine patterns ofsemiconductor devices, in that a primary electron beam is directedobliquely onto a specimen. The apparatus disclosed in JP-2001-15055intentionally directs a primary electron beam out of the axis of anobjective lens to generate chromatic aberration, and also uses anelectrostatic and magnetic multipolor to generate chromatic aberrationwhich has the same magnitude as but a different direction from theformer chromatic aberration to cancel out the chromatic aberration, sothat SEM images can be provided at a high resolution even under a lowaccelerating voltage condition which involves a large beam inclination.Further, the primary electron beam is controlled to be deflected at alltimes about an object point on the optical axis of the objective lens inorder to minimize the off-axis aberration of the objective lens.However, the field-cannot be moved unless the object point is displaced,but a movement of the object point will result in increased off-axisaberration of the objective lens. Thus, the image-shift is essentiallydifferent from the beam tilting.

In the present invention, the ratio of an object point of an objectivelens to an inclination of a primary electron beam at an image point isdefined as the “objective lens axis.” The objective lens axis may beexemplified by a current center axis which is generally known by usersof charged particle beam apparatuses. The objective lens axis, asreferred to in the present invention, does not exist in the beam tiltingsince the object point is at center in the beam tilting.

It is therefore an object of the present invention to provide a chargedparticle beam apparatus which accomplishes an objective lens axis with areduced degradation in the resolution due to chromatic aberration evenwith an image-shift of ±75 μm or more, and a defect inspection apparatuswhich has a CAD navigation function associated with an image-shiftfunction.

The present invention relates to a technique that the coordinate userfor using the coordinates for converting an image-shift moving amount toa specimen stage (DUT stage) moving amount in communications between animage processor for processing charged particle beam images and a memoryfor storing information on circuit line pattern, is introduced into theCAD navigation function, in the defect inspection apparatus whichcombines probes with a charged particle beam apparatus.

For example, as to a defect inspection apparatus for measuring electricproperties of a specimen having a fine circuit line pattern formed on awafer, wherein a charged particle beam apparatus includes a plurality ofprobes configured to be brought into contact with a plurality of padsconnected to the circuit line pattern or with plugs to measure electricproperties of the specimen, means for irradiating the specimen with acharged particle beam, image-shift means for moving a spot irradiatedwith the charged particle beam on the specimen, means for detecting asecondary charged particle beam generated from the specimen byirradiating the specimen with the charged particle beam to capture animage of the specimen, display means for displaying the image, inputmeans for specifying an arbitrary location on the image, storing meansfor storing information on the circuit line pattern, image processingmeans for processing the captured image for displaying the image on thedisplay means, and communication means for interconnecting the storingmeans and the image processing means, wherein the defect inspectionapparatus displays the circuit line pattern and the captured image onthe display means, displays information for requesting a user to specifythe same location on the circuit line pattern and on the captured image,and communicates information on coordinates of a specified positionbetween the storing means and the image processing means, and thecoordinate information includes positional information of the chargedparticle beam on the specimen by the image-shift means, therebyachieving the aforementioned object.

The present invention significantly improves the user's convenience.Specifically, the present invention can provide a charged particle beamapparatus which reduces a degradation in resolution even with animage-shift of ±75 μm or more, and a defect inspection apparatus whichhas a CAD navigation function associated with an image-shift function.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertically sectional view illustrating an exemplaryconfiguration of a defect inspection apparatus;

FIG. 2 is a schematic diagram illustrating in detail electron opticselements in the defect inspection apparatus illustrated in FIG. 1;

FIG. 3 is a schematic diagram illustrating a graphical user interface(GUI) associated with a personal computer (PC) for controlling a SEM ofthe defect inspection apparatus;

FIGS. 4A to 4C are diagrams each illustrating an exemplary SEM screen onthe PC for controlling the SEM of the defect inspection apparatus;

FIGS. 5A to 5C are diagrams each illustrating a GUI for an image-shiftunit of the PC for controlling the SEM of the defect inspectionapparatus;

FIG. 6 shows an exemplary message which is displayed when an image-shiftoperation amount exceeds a set value;

FIGS. 7A and 7B are flow charts illustrating in combination a basic flowof image-shift control in the defect inspection apparatus illustrated inFIG. 1;

FIG. 8 is a flow chart illustrating a basic flow of image-shift controlin the defect inspection apparatus illustrated in FIG. 1;

FIG. 9 is a conceptual diagram representing the relationship between DUTstage coordinates and image-shift DAC coordinates;

FIG. 10 is a conceptual diagram representing the relationship betweenimage-shift operational coordinates and image-shift DAC coordinates; and

FIGS. 11A and 11B are conceptual diagrams for describing a field offsetassociated with an image-shift axis correction.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following, one embodiment of the present invention will bedescribed with reference to the accompanying drawings. FIG. 1illustrates an exemplary configuration of a defect inspection apparatus,and FIG. 2 illustrates an exemplary configuration of a scanning electronmicroscope (hereinafter called the “SEM”). First, the configuration ofthe defect inspection apparatus will be described with reference to FIG.1.

SEM electron optics elements, generally designated by 101, make up anillumination optical system for irradiating a primary electron beam 103onto a specimen and scanning the primary electron beam 103 on thespecimen. Therefore, an electron gun 101 in this embodiment means asystem which includes all components required for the SEM, such as anelectron source for generating electron beams, a deflector for scanninga beam, lenses for focusing an electron beam, and the like. A vacuumchamber partition 102 separates an atmospheric area from a vacuum area.The operation of the SEM electron optics elements 101, for example, anelectron beam extracting voltage for the electron source, currentsapplied to the deflector and lenses, and the like are controlled by anelectron optics controller 116.

Secondary electrons 105 generated from a specimen 118 under inspectionirradiated with the primary electron beam 103 are detected by asecondary electron detector 104. The secondary electron detector 104comprises a sensor unit disposed within the partition 102 for actuallydetecting electrons, and a base unit projected out of the partition 102,to which wires are connected for connection to a power supply. Amechanical probe 106 is held by an attachment 107, and is brought intocontact with a predetermined region of a specimen under inspection. Aprobe driving means 108, for moving the attachment 107 to a desiredposition, moves the mechanical probe 106 together with the attachment107 to a desired position.

A specimen, which is actually subjected to a defect inspection, is heldon a specimen holder 109. The specimen holder 109 in turn is held by aspecimen holder driving means 110. The specimen holder 109 and specimenholder driving means 110 are collectively called the “DUT stage.” TheDUT stage and probe driving means 108 are formed on a base stage 111which comprises a driving means for integrally driving the DUT stage andprobe driving means 108 in X and Y (in-plane), and Z (vertical)directions. The integral formation of the DUT stage and probe drivingmeans 108 on the base stage 111 is one feature of this embodiment. Animportant aspect, from a viewpoint of technical idea, is to configurethe apparatus such that both the specimen 118 under inspection andmechanical probe 106 can be moved independently of each other as well asintegrally with each other. The base stage 111 is further carried on abase 112.

The specimen holder 109 and attachment 107 are connected to anelectrical property measuring device 113. The electrical propertymeasuring device 113 mainly measures the current-voltage property of aspecimen detected by the mechanical probe 106, to calculate a desiredproperty value from the measured property, for example, a resistance, acurrent value, a voltage, and the like at a location of the specimen incontact with the mechanical probe 106. For use in analyses onsemiconductor wafers, a semiconductor parameter analyzer may be used, byway of example, for the electrical property measuring device 113. Theelectrical property measuring device 113 is connected to the specimenbase 109 because a power supply plug may be provided on a specimencarrying surface of the specimen holder 109 for applying a current or avoltage to the specimen.

The property value measured by the electrical property measuring device113 is transmitted to a control computer 114 through a transmissionline. The control computer 114 makes a higher analysis based on theinformation transmitted thereto. For example, the control computer 114analyzes the measured value to determine whether a measured site isdefective or normal. The control computer 114 is provided with a storingmeans such as an optical disk drive, a hard disk drive, a memory or thelike, so that the measured electrical property value can be stored inthe storing means. The control computer 114 also serves to control theoperation of the overall defect inspection apparatus. For example, theelectronic gun controller 116, secondary electron detector 104, probedriving means 108, specimen unit, and base stage 111 operate under thecontrol of the control computer 114.

For the purposes mentioned above, the control computer 114 comprises amemory 115 for storing software for controlling each of componentsconnected to the control computer 114, and an input means for the userto enter set parameters for the defect inspection apparatus. The inputmeans may be, for example, a keyboard, a mouse for moving a pointer onan operation screen, and the like. Data on the wiring layout of aspecimen under inspection (hereinafter called the “CAD image data”) isstored in CAD workstation (WS) 110. The CAD WS 117 comprises an imagedisplay means for displaying a wiring layout. The CAD WS 117 isconnected to the control computer 114, and transmits, as required, CADimage data to the control computer 114.

A SEM control personal computer (PC) 119 controls optical conditions,magnification, focusing, and image-shift for the SEM, the brightness ofSEM images, scan speed, alignment, recording of images, movements of thestage and/or probe, and the like in response to operations performed onand commands entered through a graphical user interface (hereinaftercalled the “GUI”) of the PC or WS. A control panel 120 implements someof functions of the SEM control PC 119, mechanical probe 106, specimenunit, and base stage 111 through operations with knobs, joystick,buttons and the like. It will be apparent that the SEM control PC 119may be embodied in a work station.

Referring next to FIG. 2, there is illustrated an exemplaryconfiguration of the SEM electron optics elements. A primary electronbeam 208 emitted and accelerated by an electron gun 201 is focused by acondenser lens 202 in front of an aperture 203. The amount of theprimary electron beam 208 passing through the aperture 203 can beadjusted by controlling the position at which the primary electron beam208 is focused by the condenser lens 202. The primary electron beam 208,which has passed through the aperture 203, receives a deflecting actionapplied by image-shift coils 204, 205 and passes through an objectivelens 209, and is irradiated onto a specimen 210. The image-shift coils204, 205 may be operated independently of each other, or operated with aconstant deflection ratio of the upper and lower image-shift coils. Inany case, the primary electron beam 208 can be irradiated to thespecimen 210 at a different position by adjusting the image-shift coils204, 205. This operation is generally called a “beam shift” or“image-shift.” Alignment coils 206, 207 are normally adjusted to passthe primary electron beam 208 through a desired axis of the objectivelens 209. Also, during an image-shift operation, the alignment coils206, 207 can adjust an object point 211 of the objective lens 209 tocorrect a field offset during the image-shift operation. This correctiveoperation will be described later in greater detail.

FIG. 2 merely illustrates an exemplary configuration of the SEM electronoptics elements. For example, a second condenser lens may be insertedfor controlling a convergence angle of the primary electron beam 207 onthe specimen 206 after it has passed through the aperture 203. Also,while the secondary electron detector 104 is mounted on the vacuumchamber partition 102 in FIG. 1, a filter and a secondary electrondetector may be disposed above the objective lens to extract and detectsecondary electrons in a direction opposite to the direction in whichthe primary electron beam 207 travels. Further, a boosting electrode maybe arranged along the optical axis for improving the resolution.

Referring next to FIG. 3, description will be made on an exemplarygraphical user interface (GUI) displayed on the SEM control PC 119 ofthe defect inspection apparatus illustrated in FIG. 1. The GUI 301 onthe SEM control PC 119 is mainly composed of seven windows. A SEMcontrol GUI window 302 contains icons or a menu of SEM image display,settings of optical conditions for the SEM, magnification of the SEM,focus, image-shift, brightness of SEM images, scan speed, alignment,image recording, and the like. A base stage control GUI window 303contains an icon for moving the base stage 111 to a central position, aCCD observation position, a position at which the mechanical probe 106is exchanged, and the like, an icon for removing backlash, andcoordinate input/display boxes. A DUT stage control GUI window 304contains a cross cursor indicative of a location to which a probe ismoved, an arrow-shaped icon, a combo-box for selecting a moving amount,and coordinate input/display boxes. An image-shift control GUI window305 contains a cross cursor indicative of a location to which a probe ismoved, an arrow-shaped icon, a combo-box for selecting a moving amount,coordinate input/display boxes, and a reset button for returning to animage-shift midpoint, and the like. A coordinate memory display GUIwindow 306 contains an icon for registering the base stage coordinates,DUT stage coordinates, and image-shift coordinates in the memory, acombo-box for selecting and calling registered coordinates, andregistered coordinate display boxes. A movement selection GUI window 307contains an icon for selecting any of the base stage, DUT stage, andshifted image for movement, and a lock icon for preventing any of thebase stage, DUT stage, and shifted image from moving. Assume that theforegoing GUI windows are combined into a SEM-stage control GUI complex.

A probe control GUI window 308 for controlling the driving of themechanical probe 106 contains an icon for selecting and displaying aprobe unit which the user wishes to drive; an icon for fully retractinga probe; a scroll bar and arrow-shaped icons for driving probes X, Y, Zusing a mouse; a scroll bar for finely adjusting a probe driven in theZ-direction with the mouse; reset icons for returning probes X, Y, Z totheir respective midpoints; a combo-box for selecting micromotion movingspeeds for the probes X, Y, Z; a combo-box for selecting increments forthe probes X, Y, Z; a combo-box for selecting a continuous moving speedfor the probes X, Y, Z; and a driving state display section for eachprobe. The probe control GUI window 308 substantially occupies the righthalf of the GUI 301 on the SEM control PC 119 because a large scroll baris displayed on the GUI in order to improve the accuracy of operationson the scroll bar through the mouse for driving the probes X, Y, Z.

In FIG. 3, the SEM-stage control GUI complex is displayed on the leftside of the GUI, while the probe control GUI window 308 is displayed onthe right side, but the SEM-stage control GUI complex and the probecontrol GUI window 308 may be interchanged in place therebetween if sucha change facilitates the user's observation and operations.

FIGS. 4A, 4B, 4C illustrate examples of SEM images displayed on the SEMcontrol GUI window 302. In the example illustrated in FIG. 4A, when fourprobes are used to conduct a defect inspection, four probes are includedin the SEM screen field. The probe unit is operated such that a probe401 is brought into contact with a target plug 405 of a plurality ofplugs 409, and a probe 402 is brought into contact with a target plug406. A probe 403 has already been in contact with a target plug 407. Aprobe 404 is brought into contact with a target plug out of the SEMfield 410. In the situation illustrated in FIG. 4A, the SEM field 410includes the three probes which should be brought into contact withtarget plugs, in which case the stage need not be moved, or noimage-shift operation is required.

In the example illustrated in FIG. 4B, three probes have already been incontact with their respective target plugs. However, a target gate plug408 associated with the probe 404 is out of the SEM field 410. In thisevent, the stage cannot be moved because of mechanical vibrationspossibly associated therewith, which could damage the probes in contact.While the stage may be slowly moved in order to prevent damages of theprobes, the probes can come off their contacts with the respectivetarget plugs while the stage is being moved, due to a creep phenomenonof piezo devices which are used for driving the probes in order toachieve a positioning resolution of 5 nm or le ss. From the reasons asmentioned above, it is optimal to rely on an image-shift operation tomove the SEM field 410. An arrow 411 is displayed to clarify thedirection in which one can find the probe 404 that is selected fordriving. The direction in which the arrow is oriented varies dependingon the direction in which a probe is driven.

In the example illustrated in FIG. 4C, an image-shift operation has beenperformed such that the probe 404 and target gate plug 408 can beobserved within the SEM field 410. Current semiconductor devices haveplugs, the size of which is 200nm or less, while a magnification of theSEM for observation is approximately 10 k. With this magnification, anobservation field extends approximately to 10 μm. For example, a currentsemiconductor memory mat has a sector width which is approximately 150μm at most. If the sector width is made larger to increase the memorycapacity, the response degrades due to high frequency components of thedevice, so that a larger capacity is accomplished by reducing the pitchof a plurality of plugs 409. The target gate plug 408 is located at theend of one side of the sector for pullup, and assuming that theremaining target plugs 402–405 which one wishes to inspect are locatedat the opposite end of the sector, the target plugs can be observed withthe SEM over the entire range without moving the DUT stage as long as animage-shift moving amount of 150 μm or ±75 μm is satisfied. Aconventional SEM may perform an image-shift operation after adjustmentsof electron optics elements to avoid observing possible contaminationswhich can stick to the elements during the adjustments of the electronoptics elements when the SEM is set to an observation magnification of50 k or higher for a resolution specimen (like good particles on carbonmaterials) or the like, and an image-shift moving amount should beapproximately 15 μm at most in order to avoid a degradation in theresolution due to off-axis aberration associated with the image-shiftoperation, and particularly due to deflection chromatic aberration at alow accelerating voltage. Also, for purposes of avoiding observation ofcontaminations, coordinate positions need not be displayed after theimage-shift operation.

However, the defect inspection apparatus lays out a SEM image and a CADimage, so that the defect inspection apparatus is required to have afunction for allowing the CAD image to follow a change in the SEM imagecaused by an image-shift operation, and must have the ability to displayan image-shift moving amount in coordinates because there can be arequest to bring a probe into contact with a plug located at certainpitches away, even when the CAD image is not used. In the following,this coordinate display capabilities will be described with reference toFIGS. 5A, 5B, 5C.

FIG. 5A illustrates an example of an image-shift control GUI. DUT stageconversion coordinates 501 are coordinates of the DUT stage when animage-shift moving amount is converted to a DUT stage moving amount, andare transmitted to the CAD WS 117 or transmitted from the CAD WS 117. ACAD layout image has an area as wide as 10 mm×10 mm, so that even amovement over ±75 μm through an image-shift operation cannot accomplisha movement of the SEM image to fit to the entire CAD layout imagethrough the image-shift operation. Also, a linear scale may be used forthe DUT stage to accurately correspond a CAD layout image to the DUTstage coordinates. For this reason, the image-shift coordinates areconverted to the DUT stage coordinates which are used for observations.Image-shift operational coordinates 502 are coordinates for representingan image-shift moving amount which is converted from coordinates atwhich the image-shift drives (image-shift DAC coordinates) tocoordinates at which an operation (observation) is being actually underway, because a raster rotation function is operating for rotating theSEM image field, the image-shift operational coordinates 502 arerequired because they are different from the image-shift DACcoordinates. Since the SEM involves an objective lens rotating action,the raster rotation function is operated at all time to control suchthat a direction in which the DUT stage is moved matches a direction inwhich the SEM scans. When the user follows the pitch, the userreferences the image-shift operational coordinates. Details on thecoordinate conversion will described later.

An RST 503 is a button for returning a shifted image to a midpoint. Anyof hollow triangular arrow buttons 504, when clicked, causes an image toshift in a direction indicated by the clicked arrow button 504 by amoving amount selected in a combo-box 505. The user can enter a desiredmoving amount into the combo-box 505. A cross cursor 506 permits theuser to visually know an actual coordinate position. Image-shiftcoordinates are displayed in coordinate boxes 507, or appropriate valuesmay be directly entered into the coordinate boxes 507 to shift an imageto a desired position. The function described herein is effective tocoordinates selected by an option button.

FIG. 5B illustrates another example of the image-shift control GUI. Theimage-shift control GUI of FIG. 5B additionally comprises a pitchinterval entry box 508, and counter boxes 509 for displaying the numbersof pitches in the X- and Y-directions, respectively, in addition to thefunctions shown in FIG. 5A. When the user enters a pitch into the entrybox 508 and performs an image-shift operation, an integer part of theratio of an image-shift moving amount to the pitch is displayed in thecounter box 509 for each of the X- and Y-directions. Alternatively, whenthe user enters the number of pitches by which the user wishes to movean image, and performs an image-shift operation, a message 601 as shownin FIG. 6 is displayed in a message area 602 when a set number of counts(number of pitches) is reached. A click on a mouse in a Yes area 603causes an image-shift operation to continue, whereas a click on a mousein a No area 604 results in rejection of the image-shift operation.Since user always performs the image-shift operation for the SEM imagefield, the counter function is effective only when the image-shiftoperational coordinates are selected by the option button.

FIG. 5C is an example of the image-shift control GUI which limits thecross cursor, arrow-shaped buttons, combo-box, and counter function onlyto the image-shift operational coordinates, and displays the specimenconversion coordinates only as reference values. These limitations areplaced because the user always operates on the image-shift operationalcoordinates, except for the entry of coordinates, the DUT stageconversion coordinates are meaningful when a communication is made withthe CAD WS 117, and the processing is performed within the controlcomputer 114.

Next, description will be made on a method of operating the defectinspection apparatus illustrated in FIG. 1 using the electron opticscomponents illustrated in FIG. 2. Assume in the following descriptionthat positional information has already been calibrated for CAD imagedata and SEM image data. Details on a coordinate conversion method willbe described later.

First, a method of calibrating positional information will be describedin brief. The DUT stage is roughly moved to a position corresponding toa point on a certain pattern in a CAD image, and the DUT stage is finelyadjusted, while observing on a SEM image, such that the same patternappears at the center of the screen, to perform an alignment of CADcoordinates to the DUT stage coordinates at a first point. Next, the DUTstage is roughly moved to a position corresponding to a point on anotherpattern in the same CAD image, and the DUT stage is finely adjusted,while observing on the SEM image, such that the same pattern appears atthe center of the screen, to perform an alignment of the CAD coordinatesto the DUT stage coordinates at a second point. Finally, the DUT stageis roughly moved to a position corresponding to a point on a furtherpattern on the same CAD image, and the DUT stage is finely adjusted,while observing on the SEM image, such that the same pattern appears atthe center of the screen to perform an alignment of the CAD coordinatesto the DUT stage coordinates at a third point. The foregoing operationspermit a correspondence to be established between the CAD coordinatesand DUT stage coordinates. During the alignment operation, the SEM-basedobservation may be performed at a low magnification of 100 or lower whenthe DUT stage is roughly moved, and at a high magnification ofapproximately 10 k when the DUT stage is finely adjusted. The alignmentsare preferably performed at three points near corners of the specimen inorder to increase the accuracy of the conversion from the CADcoordinates to the DUT stage coordinates over the entire specimen.

Referring first to FIGS. 7A, 7B, description will be made on animage-shift operation made by the user through the GUI of the PC 119, orwith associated knobs and joystick of the control panel 120.

As the user performs an image-shift operation through the GUI of the SEMcontrol PC 119 or with associated knobs and joystick of the controlpanel 120 (step 701), an operating amount is transmitted to the controlcomputer 114 which calculates a DAC changing amount for an image-shiftXY. The control computer 114 also calculates a DAC amount of theimage-shift XY from a coordinate input amount (step 702). For the DACchanging amount, the control computer 114 adds the DAC changing amountto a current DAC amount or subtract the DAC changing amount from thecurrent DAC amount. Once the DAC amount is determined, the image-shiftis actually performed through the electron optics control means 116(step 703). Also, the control computer 114 calculates the coordinates onthe image-shift DAC axes from an actually set image-shift DAC value(step 704).

Subsequently, two different sequence of steps may be contemplated. Afirst sequence of steps converts the image-shift DAC coordinates to theDUT stage coordinates, and a second sequence of steps converts theimage-shift DAC coordinates to the image-shift operation axes. Firstdescribed is the sequence of steps for converting the image-shift DACcoordinates to the DUT stage coordinates.

The control computer 114 converts the image-shift DAC coordinates to theDUT stage coordinates (step 705). The converted coordinate values aretransmitted to the SEM control PC 119 for displaying the coordinates onthe GUI (step 706). In this event, when the CAD WS 117 is not linked tothe SEM control PC 119 so that a CAD layout image is not overlaid on aSEM image (step 707), it is determined again whether or not animage-shift operation occurs (step 716).

Conversely, when the CAD WS 117 is linked to the SEM control PC 119 sothat the CAD layout image is overlaid on the SEM image (step 707), thecontrol computer 114 converts the DUT stage coordinates to CADcoordinates and transmits a moving amount to the CAD WS 117 (step 708)before it receives a new CAD image from the CAD WS 117 (step 709), andoverlays the CAD image on the GUI of the SEM control PC 119 (step 710).Subsequently, the flow proceeds to step 707. It is determined againwhether or not an image-shift operation occurs (step 716), and theprocessing is terminated when no image-shift operation occurs (step716), or the flow returns to step 702 when the image-shift operationoccurs (step 716), such that the control computer 114 again performssimilar processing to the foregoing.

Next described is the sequence of steps for converting the image-shiftDAC coordinates to the image-shift operation axes. The control computer114 converts the image-shift DAC coordinates to the image-shiftoperational coordinates (step 711). Then, the control computer 114transmits the converted coordinate values to the SEM control PC 119 fordisplaying the coordinates on the GUI (step 711).

The control computer 114 determines whether or not the counters havebeen set on the image-shift operational coordinate axes on the SEMcontrol PC 119 for displaying the number of pattern widths by which amovement has been made in the X- and Y-directions, respectively. Whenthe counters are not set (step 713), the flow proceeds to step 707.Conversely, when the counters have been set (step 713), the controlcomputer 114 calculates the ratio of each of the calculated image-shiftoperational coordinates to the pattern width selected on the GUI of theSEM control PC 119, removes the decimal point from the calculated ratio,and defines the resultant value as a count value in the X- orY-direction (step 714). The control computer 114 transmits the countvalues to the SEM control PC 119 for display on the GUI (step 715).Subsequently, the flow proceeds to step 707.

Also, the SEM control PC 119 sets the number of pattern widths by whicha movement is made in each of the X- and Y-directions, or the SEMcontrol PC 119 sets an image-shift amount by which a movement is made oneach of the image-shift operational coordinate axes, and the controlcomputer 114 compares actual count values with the set values. When theset values are exceeded by the actual count values, the image of FIG. 6is displayed for permitting the user to determine whether or not theimage-shift operation is continued.

Referring next to FIG. 8, description will be made on the image-shiftoperation when the user moves a layout pattern on the CAD WS 117.

A moving amount by which a layout pattern has been moved on the CAD WS117 is transmitted to the control computer 114 (step 801). The controlcomputer 114 calculates a moving amount on the image-shift coordinates,as converted to the DUT stage axes (step 802). When the specimenconversion coordinates are directly inputted on the GUI of the SEMcontrol PC 119, the control is started from this moment (step 803).Next, the moving amount is transmitted to the control computer 114 whichcalculates a moving amount on the image-shift DAC axes. The controlcomputer 114 also calculates input coordinate values on the image-shiftDAC axes from the input coordinate amounts (step 804). Next, the controlcomputer 114 calculates a DAC change amount from the moving amount, andadds the calculated DAC change amount to a current DAC amount orsubtracts the DAC change amount from the current DAC amount. The controlcomputer 114 calculates the DAC amount from the input coordinate values.Once the DAC amount is determined, an image-shift is actually performedthrough the electron optics control means 116 (step 805). Also, thecontrol computer 114 again calculates the coordinates on the image-shiftDAC axes from the actually set image-shift DAC value (step 806).

The control computer 114 converts the image-shift DAC coordinates to theDUT stage coordinates (step 807). The converted coordinate values aretransmitted to the SEM control PC 119 for displaying the coordinates onthe GUI (step 808). In this event, when the CAD WS 117 is not linked tothe SEM control PC 119, so that the CAD layout image is not overlaid onthe SEM image (step 809), the processing is terminated (step 813).

Conversely, when the CAD WS 117 is linked to the SEM control PC 119, sothat the CAD layout image is overlaid on the SEM image (step 809), thecontrol computer 114 converts the DUT stage coordinates to the CADcoordinates and transmits a moving amount to the CAD WS 117 (step 810)before it receives a new CAD image from the CAD WS 117 (step 811), andoverlays the CAD image on the GUI of the SEM control PC 119 (step 812),followed by termination of the processing (step 813).

By executing the foregoing steps, a CAD image and coordinates overlaidon the GUI of the SEM control PC 119 can be automatically updatedfollowing a change in the SEM image field resulting from an image-shiftoperation, thus significantly reducing a burden on the user during theprobing.

Next, description will be made on the coordinate conversion associatedwith the image-shift described in the foregoing embodiment. Thefollowing six sets of coordinates should be taken into consideration inthe image-shift control:

(1) DUT stage coordinates (x_(DUT), y_(DUT));

(2) Image-shift coordinates converted to DUT stage (x_(IS-DUT),y_(IS-DUT));

(3) Image-shift axis correction coordinates (X_(IS), Y_(IS));

(4) Ideal image-shift coordinates (x_(IS), y_(IS));

(5) Image-shift DAC coordinates (x_(IS-DAC), y_(IS-DAC)); and

(6) Image-shift operational coordinates (x_(IS-OP), Y_(IS-OP)).

The DUT stage coordinates (1) and image-shift coordinates converted tothe DUT stage (2) are basically completely the same coordinates if thelinearity and orthogonality can be ignored for the DUT stage. Theimage-shift axis correction coordinates (3) are coordinates convertedwhen an image-shift coil is ideally disposed. The ideal image-shiftcoordinates (4) are similar to the image-shift axis correctioncoordinates (3), and are coordinates which are converted inconsideration of a field offset which occurs when an off-axis due to animage-shift is corrected. The image-shift DAC coordinates (5) arecoordinates converted when the orthogonality of the image-shift coildeviates from an ideal axis in the ideal image-shift coordinates (4).The image-shift operational coordinates (6) are coordinates converted tofit the coordinate axes of the image-shift axis correction coordinates(3) to the SEM scan axis, and are used for correcting the rotation ofthe scan axis caused by excitation of the objective lens to thecoordinate axes of the DUT stage, and for electrically rotating the scanaxis.

As described in connection with FIGS. 7A, 7B, 8, conversion incoordinates required for controlling an image-shift operation involvethe relationships of a conversion between the coordinates (x_(IS-DUT),y_(IS-DUT)) (2) and the coordinates (x_(IS-DAC), y_(IS-DAC)) (5) and aconversion between the coordinates (x_(IS-OP), y_(IS-OP)) (6) and thecoordinates (x_(IS-DAC), y_(IS-DAC)) (5) The respective relationships ofthe coordinate conversions are described in FIGS. 9 and 10,respectively. The respective coordinate conversions can be expressed inmathematical formulae as follows:

$\begin{matrix}{{\begin{pmatrix}x_{{IS} - {DUT}} \\y_{{IS} - {DUT}}\end{pmatrix} = {A\begin{pmatrix}X_{IS} \\Y_{IS}\end{pmatrix}}}{\begin{pmatrix}X_{IS} \\Y_{IS}\end{pmatrix} = {B\begin{pmatrix}x_{IS} \\y_{IS}\end{pmatrix}}}{\begin{pmatrix}x_{IS} \\y_{IS}\end{pmatrix} = {C\begin{pmatrix}x_{{IS} - {DAC}} \\y_{{IS} - {DAC}}\end{pmatrix}}}{\begin{pmatrix}x_{{IS} - {OP}} \\y_{{IS} - {OP}}\end{pmatrix} = {D\begin{pmatrix}X_{IS} \\Y_{IS}\end{pmatrix}}}} & {{Equations}\mspace{14mu} 1}\end{matrix}$

A matrix A is a matrix of linear transformation of the image-shiftcoordinates converted to the DUT stage and the image-shift axiscorrection coordinates, and depends on a rotating angle due toexcitation of the objective lens. A matrix B is a matrix of lineartransformation of the image-shift axis correction coordinates and idealimage-shift coordinates, and is a matrix which takes into considerationa field offset which occurs when an off-axis during an image-shiftoperation is corrected by a single alignment coil or image-shift coil. Amatrix C is a matrix of linear transformation of the ideal image-shiftcoordinates and image-shift DAC coordinates, and depends on anorthogonality angle of the image-shift coil. A matrix D is a matrix oflinear transformation of the image-shift operational coordinates andimage-shift axis correction coordinates, and depends on an electricrotating angle of the scan axis due to raster rotation in addition to arotating angle due to excitation of the objective lens. When theimage-shift axis can also be rotated, the matrix D depends on amechanical offset angle of the scan axis from the ideal image-shiftaxis.

From the foregoing relationships, transformations can be derived for (2)and (5) and for (6) and (5).

$\begin{matrix}{{\begin{pmatrix}x_{{IS} - {DUT}} \\y_{{IS} - {DUT}}\end{pmatrix} = {{ABC}\begin{pmatrix}x_{{IS} - {DAC}} \\y_{{IS} - {DAC}}\end{pmatrix}}}{\begin{pmatrix}x_{{IS} - {DAC}} \\y_{{IS} - {DAC}}\end{pmatrix} = {({ABC})^{- 1}\begin{pmatrix}x_{{IS} - {DUT}} \\y_{{IS} - {DUT}}\end{pmatrix}}}} & {{Equations}\mspace{14mu} 2} \\{{\begin{pmatrix}x_{{IS} - {OP}} \\y_{{IS} - {OP}}\end{pmatrix} = {{DBC}\begin{pmatrix}x_{{IS} - {DAC}} \\y_{{IS} - {DAC}}\end{pmatrix}}}{\begin{pmatrix}x_{{IS} - {DAC}} \\y_{{IS} - {DAC}}\end{pmatrix} = {({DBC})^{- 1}\begin{pmatrix}x_{{IS} - {OP}} \\y_{{IS} - {OP}}\end{pmatrix}}}} & {{Equations}\mspace{14mu} 3}\end{matrix}$

Some aspects to be noted for each of matrix elements will be describedbelow.

The actual DUT stage coordinates and the image-shift coordinatesconverted to the DUT stage may suffer from a zero offset depending onthe linearity and orthogonality of the DUT stage and the positioning ofthe secondary electron detector of the SEM, and can therefore fail tofit to each other. In such a case, the zero offset can be corrected forby the following relationship:

$\begin{matrix}{\begin{pmatrix}x_{DUT} \\y_{DUT}\end{pmatrix} = {{A^{\prime}\begin{pmatrix}x_{{IS} - {DUT}} \\y_{{IS} - {DUT}}\end{pmatrix}} + \begin{pmatrix}{\Delta\; x_{{IS} - {DUT}}} \\{\Delta\; y_{{IS} - {DUT}}}\end{pmatrix}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

A matrix A′ is a matrix of linear transformation which takes intoconsideration the linearity and orthogonality of the DUT stage.Δx_(IS-DUT), Δ_(yIS-DUT) represent offset amounts of the DUT stage froma spot irradiated with a primary electron beam. In an actual apparatus,a relative movement from fixed conditions is often relied on to handlethe offset amounts. Also, in an image-shift operation in a range ofapproximately ±75 μm as compared with a wide operation range of the DUTstage extending 10 mm or more, the linearity and orthogonality of theDUT stage can be often ignored. Therefore, the matrices A and A′ aretreated as the same coordinates in the following description.

The matrices B, C comprise elements which are not prominent in a normalimage-shift range of ±15 μm, as described in connection with FIGS. 4A,4B, 4C, but are prominent when an image-shift range of ±75 μm or more isaccomplished, as required by the defect inspection apparatus, and whichmust be taken into consideration for highly accurate positional control.The matrix B can be equal with a unit matrix when a correction is addedto prevent the object point of the objective lens from being moved bytwo alignment coils or an image-shift coil. In the following, the matrixB will be described with reference to FIGS. 11A, 11B.

FIG. 11A conceptually illustrates a ray trajectory during theimage-shift control. An actual trajectory of a primary electron beam isrepresented by a ray trajectory 1. When image-shift coils 204, 205 aredriven, the ray trajectory 1 changes to a virtual ray trajectory 1. Whenan upper alignment coil 206 alone is further driven, the ray trajectory1 changes to a combination of a virtual ray trajectory 2 and a raytrajectory 2. When a lower alignment coil 207 is further driven, the raytrajectory 1 changes to a combination of a virtual ray trajectory 3 anda beam trajectory 3.

FIG. 11B only illustrates central trajectories of the ray trajectoriesshown in FIG. 11A. The primary electron beam, emitted from a primaryelectron beam crossover point (object point A1 of the objective lens) onthe surface of the objective lens, is deflected by the upper image-shiftcoil 204 (B1), is again deflected by the lower image-shift coil 205 inthe opposite direction (C1), passes through one point (D1) on the mainsurface of the objective lens, and is irradiated obliquely to anobjective lens image point (E1) on an objective lens image plane (i.e.,the specimen). As the image-shift coils are driven, the object point A1of the objective lens is shifted to A2, so that the trajectory virtuallyfollows A2–B2–C1–D1–E1. When the upper alignment coil 206 alone isdriven in this state, the object point A2 of the objective lens isshifted to A3, so that the trajectory changes to A3–B2–C2–D2–E2. Theshift of the object point A2 of the objective lens to A3 causes a shiftof the objective lens image point E1 to E2, so that the primary electronbeam is irradiated to an offset spot. Further, when the lower alignmentcoil 207 is also driven in this state to shift the object point A3 ofthe objective lens to fit to A3, the resulting trajectory followsA2–B2–C2–D3–E1. When the object point A3 of the objective lens is fittedto A2, the primary electron beam is irradiated to the original objectivelens image point E1, so that the offset of the irradiated spot can beremoved.

The image-shift in SEM is basically relied on a method of moving a spoton a specimen irradiated with a primary electron beam by deflecting theprimary electron beam using two image-shift coils. When the primaryelectron beam is deflected by an image-shift coil, the primary electronbeam obliquely impinges on a specimen, resulting in off-axis aberration.Also, chromatic aberration is produced in association with thedeflection. For minimizing the influence of such aberrations, theimage-shift control is conducted such that a desired axis is found byadjusting the ratio of currents applied to the upper and lowerimage-shift coils, or currents independently applied to the respectivecoils in the X-direction and Y-direction, respectively. Actually,however, the desired axis cannot be found only with adjustments in thesame direction by a rotating action of the objective lens. For thisreason, a single alignment coil may be provided independently of theimage-shift coils, or an alignment signal is superimposed on the upperimage-shift coil to add a correction depending on an image-shift amount,thereby achieving the identification of the desired axis.

As described above, a correction made by a single alignment coil causesa shift of the object point of the objective lens and a resulting shiftof a spot on a specimen irradiated with the primary electron beam togive rise to a field displacement, thus resulting in coordinates whichare different from those to which one wishes to actually shift theprimary electron beam. In consideration of this amount, the matrix B isset in order to shift the primary electron beam to desired image-shiftcoordinates. However, it is possible to avoid the primary electron beamshifted from an intended irradiated spot on the specimen and remove thefield movement by adding a correction depending on an image-shift amountto an alignment signal by providing two independent alignment coils orsuperimposing the alignment signal on the upper and lower image-shiftcoils to find the desired axis, and simultaneously conducting theimage-shift control to prevent the object point of the objective lensfrom shifting. When the field movement can be removed by this method,the matrix A can be treated as a unit matrix, without the need fortaking into consideration the matrix B, resulting in an improvement inthe coordinate conversion accuracy.

The desired axis, herein referred to, may be exemplified by a currentcenter axis. The current center axis refers to an axis on which a changein excitation of an objective lens does not cause a change in theposition of the image point of the objective lens. Among the off-axisaberrations, astigmatism can be corrected by an astigmatism correctingcoil, not shown in FIG. 2, while field curvature aberration can becorrected by adjusting the excitation of the objective lens. Thoughdepending on the characteristics of a particular objective lens andelectron optics conditions, an image-shift of 100 μm will cause comaaberration of approximately 2–3 nm to leave on the current center axis.However, it is chromatic aberration resulting from the image-shift,which exerts larger influences. Specifically, the chromatic aberrationis prominent particularly at low accelerating voltages equal to or lowerthan 5 kV. For example, in a charged particle beam apparatus which isequipped with a field emission electron source having an energy spreadof 0.3 eV, an image-shift of 100 μm at an accelerating voltage of 2 kVcauses chromatic aberration of approximately 14 nm. Particularly, in thedefect inspection apparatus which is intended for semiconductormaterials as specimen, observations at low accelerating voltages areessential in order to minimize damages to specimen. Thus, an axis,called the “achromatic axis,” which can remove off-axis chromaticaberration and deflection chromatic aberration of an objective lens, canbe assumed as a desired axis. The aberrations given herein as examplesdiffer from one charged particle beam apparatus to another, as will beapparent to users of charged particle beam apparatuses.

For conditions to find a desired axis, the current center axis isgenerally well known in charged particle beam apparatuses. In thefollowing, the achromatic axis will be described in detail withreference to appropriate equations.w ₀ =a·w′ ₀  Equation 5where wo, wo′ are the position and inclination of the primary electronbeam on the surface of the objective lens, and a represents conditionsfor a desired axis. The position wi and inclination wi′ of the primaryelectron beam on the image plane of the objective lens can be expressedby the following equations using Equation 5:w _(i) =a·g _(i) ·w′ ₀w′ _(i)=(a·g′ _(i) +h′ _(i))·w′ ₀  Equations 6where gi, hi, gi′, hi′ are the positions and inclinations at the imagepoints of two paraxial rays well known in the charged particle theory.In the charged particle theory, chromatic aberration of a primaryelectron beam obliquely incident on an objective lens is expressed bythe following equation:

$\begin{matrix}{{\Delta\; w_{c}} = {\left\{ {{C_{c\; 0} \cdot w_{i}^{\prime}} + {\left( {C_{cm} + {jC}_{cr}} \right) \cdot w_{i}}} \right\} \cdot \left( \frac{\Delta\; V}{V} \right)}} & {{Equation}\mspace{14mu} 7}\end{matrix}$where Cco is an axial chromatic aberration coefficient, Ccm is amagnification chromatic aberration coefficient, Ccr is an anisotropicchromatic aberration coefficient, V is the energy of the primaryelectron beam on the objective lens image plane, and ΔV is variations inthe energy of the primary electron beam. An image-shift causesvariations ΔV in the energy which result in variations in the positionto which the primary electron beam propagates. The variations can beregarded as a type of aberration, which is called the “deflectionchromatic aberration.” This deflection chromatic aberration is notincluded in Equation 7. For example, in a charged particle beamapparatus equipped with a field emission electron source having anenergy width of 0.3 eV, an image-shift of 100 μm at an acceleratingvoltage of 2 kV causes deflection chromatic aberration of approximately8 nm, as compared with the chromatic aberration expressed by Equation 7which is approximately 6 nm. While it is possible to find from Equation7 axial conditions under which the chromatic aberration disappears,deflection chromatic aberration of 8 nm remains in the foregoingexample. It is therefore necessary to find an axis a which satisfiesconditions under which the chromatic aberration is eliminated, inconsideration of the deflection chromatic aberration as well. Thechromatic aberration produced by a deflecting action such as theimage-shift can be expressed by the following equation:

$\begin{matrix}{{{\Delta\; w_{def}} = {{C_{def} \cdot r_{IS} \cdot \left( \frac{\Delta\; V}{V} \right)} = {C_{def} \cdot a \cdot g_{i} \cdot w_{0}^{\prime} \cdot \left( \frac{\Delta\; V}{V} \right)}}}{{where}\text{:}}} & {{Equation}\mspace{14mu} 8} \\{{{C_{def}\left( {{MAGNETIC}\mspace{14mu}{FIELD}} \right)} = {{- \frac{1}{2}} \cdot \left( \frac{V}{V_{def}} \right)}}{{C_{def}\left( {{ELECTRO}\text{-}{STATIC}\mspace{14mu}{FIELD}} \right)} = {- \left( \frac{V}{V_{def}} \right)}}} & {{Equations}\mspace{14mu} 9}\end{matrix}$where C_(def) is a chromatic aberration coefficient due to deflection,and takes different values for magnetic deflection and electro-staticdeflection, ris is an image-shift operation amount, and Vdef is theenergy of the primary electron beam at a deflected location. CombiningEquation 9 with Equation 10 results in the following equation:

$\begin{matrix}{{\Delta\; w_{c}} = {\left\{ {{C_{c\; 0} \cdot \left( {{a \cdot g_{i}^{\prime}} + h_{i}^{\prime}} \right)} + {\left( {C_{cm} + {jC}_{cr}} \right) \cdot a \cdot g_{i}} + {C_{def} \cdot a \cdot g_{i}}} \right\} \cdot w_{0}^{\prime} \cdot \left( \frac{\Delta\; V}{V} \right)}} & {{Equation}\mspace{14mu} 10}\end{matrix}$The axis a which satisfies the condition for deriving zero from Equation10 is the achromatic axis which can be expressed by the followingequation:

$\begin{matrix}{a = {- \frac{C_{c\; 0} \cdot h_{i}^{\prime} \cdot}{{C_{c\; 0} \cdot g_{i}^{\prime}} + {\left( {C_{cm} + C_{def}} \right) \cdot g_{i}} + {{jC}_{cr} \cdot g_{i}}}}} & {{Equation}\mspace{14mu} 11}\end{matrix}$

Among the equations described above, wo, wo′, wi, wi′, a, rIS takecomplex numbers, while the remainings take real numbers. Also, theexemplary values given above differ depending on the characteristics ofthe objective lens.

As previously described, a correction depending on an image-shift amountis added to an alignment signal to create an achromatic axis byproviding two independent alignment coils or superimposing an alignmentsignal on the upper and lower image-shift coils, and simultaneously,control is conducted to prevent the object point of the objective lensfrom shifting, thereby making it possible to avoid the primary electronbeam irradiated to a shifted position on a specimen and effectivelyeliminate the chromatic aberration.

Published Japanese Translation of PCT International Publication forPatent Application WO 01/033603 describes an E×B field generator, i.e.,an apparatus which generates an energy distribution, which has the samemagnitude as and a direction reverse to off-axis/deflection chromaticaberration corresponding to an image-shift amount, using a wien filterto cancel out aberration. The use of this strategy will result in therealization of a current center axis of the objective lens to reduceoff-axis aberration such as coma aberration and an additional reductionin off-axis/deflection chromatic aberrations. Presumably, the use of theE×B field generator may involve a complicated configuration and controlof the apparatus and a high cost.

Finally, description will be made on coordinate conversion used incommunications between the SEM control PC 119 and CAD WS 117.Coordinates which should be taken into consideration in the CADnavigation include the following four sets:

(1) DUT stage coordinates (x_(DUT), y_(DUT));

(2) Base stage coordinates (x_(BASE), y_(BBASE));

(3) Image-shift coordinates converted to DUT stage (x_(IS-DUT),y_(IS-DUT)); and

(4) CAD navigation coordinates (x_(CAD), y_(CAD)).

The CAD navigation coordinates (4) define layout coordinates for a CADimage which has an ideal magnification and pattern information. The DUTstage coordinates (1) represent a linear scale value of the DUT stage.However, the coordinates also include an correction term for smallerrors due to backlash of stage mechanisms and the like. The base stagecoordinates (3) are coordinates resulting from a conversion from animage-shift amount to the DUT stage axis. The coordinate conversion isperformed according to the following equation:

$\begin{matrix}{\begin{pmatrix}x_{CAD} \\y_{CAD}\end{pmatrix} = {\begin{pmatrix}x_{DUT} \\y_{DUT}\end{pmatrix} + \begin{pmatrix}x_{BASE} \\y_{BASE}\end{pmatrix} + \begin{pmatrix}x_{{IS} - {DUT}} \\y_{{IS} - {DUT}}\end{pmatrix}}} & {{Equation}\mspace{14mu} 12}\end{matrix}$

When the DUT stage and base stage imply rotational misalignment and zerooffset, a conversion correction may be made in a manner similar toEquation 4.

While the foregoing embodiment has been described in connection with ascanning electron microscope which is given as an example of a chargedparticle beam apparatus, it will be apparent to developers and users ofcharged particle beam apparatuses that the same description can beapplied to a focused ion beam apparatus for observing and processingspecimen using ion beams. Also, due to the use of heavy elements such asGa ions, an electrostatic lens is used for the objective lens instead ofa magnetic lens. Thus, the matrix A in Equation 1 need not be taken intoconsideration because there is no rotating action, as experienced with amagnetic objective lens. Also, since the rotating action of theobjective lens can also be ignored in the matrix D as is the case withthe matrix A, it can be readily contemplated that the image-shiftcontrol accuracy is improved.

The present invention proposes a charged particle beam apparatus whichcan control an image-shift of ±75 μm or more without a degradedresolution due to chromatic aberration, and can display and inputcoordinates by a conversion from the stage coordinates to theimage-shift control coordinates, a conversion from the image-shiftoperational coordinates to the image-shift control coordinates, and therealization of the achromatic axis. The present invention also proposesan image-shift control method suitable for the introduction of CADnavigation into a defect inspection apparatus which is a combination ofa probe with the charged particle beam apparatus. According to thepresent invention, the user's convenience is remarkably improved whenthe user uses an image-shift function of the charged particle beamapparatus and defect inspection apparatus.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. In a defect inspection apparatus for measuring electrical propertiesof a specimen having a fine circuit line pattern formed on a wafer, acharged particle beam apparatus comprising: a plurality of probesconfigured to be brought into contact with a plurality of pads connectedto the circuit line pattern or with plugs to measure electric propertiesof the specimen; device for irradiating the specimen with a chargedparticle beam; image-shift device for moving a spot irradiated with thecharged particle beam on the specimen; device for detecting a secondarycharged particle beam generated from the specimen by irradiating thespecimen with the charged particle beam to capture an image of thespecimen; display device for displaying the image; input device forspecifying an arbitrary location on the image; storing device forstoring information on the circuit line pattern; image processing devicefor processing the captured image for displaying the image on saiddisplay device; and communication device for interconnecting saidstoring device and said image processing device, wherein said defectinspection apparatus displays the circuit line pattern and the capturedimage on said display device, displays information for requesting a userto specify the same location on the circuit line pattern and on thecapture damage, and communicates information on coordinates of aspecified position between said storing device and said image processingdevice, and the coordinate information includes positional informationof the charged particle beam on the specimen by said image-shift device.2. A charge particle beam apparatus according to claim 1, wherein: saidimage-shift device is capable of moving a spot irradiated with thecharged particle beam by 150 μm or more or by ±75 μm or more.
 3. Acharged particle beam apparatus according to claim 1, wherein: saiddisplay device displays both the captured image and the circuit linepattern.
 4. A charged particle beam apparatus according to claim 3,wherein: said display device displays the captured image and the circuitline pattern in a superimposed manner.
 5. A charged particle beamapparatus according to claim 1, wherein: said display device includesdevice for selecting DUT stage coordinates converted into a DUT stage,and image-shift operational coordinates converted from the image-shiftmoving amount into an image rotating direction in which an observationis being made.
 6. A charged particle beam apparatus according to claim5, wherein: said display device includes device for selecting animage-shift moving amount and a moving direction from previously presetcandidates, and shifting the charged particle beam to the selectedconverted coordinates.
 7. A charged particle beam apparatus according toclaim 5, wherein: said display device includes device for inputting anddisplaying the selected converted coordinates, and said charged particlebeam apparatus further comprises device for shifting the charge particlebeam to an arbitrary position on the selected converted coordinates bydirectly inputting coordinates.
 8. A charged particle beam apparatusaccording to claim 1, wherein: said display device includes device forsimultaneously displaying the DUT stage coordinates and the image-shiftoperational coordinates.
 9. A charged particle beam apparatus accordingto claim 8, wherein: said display device includes device for selectingan image-shift moving amount and a moving direction from previouslypreset candidates, and shifting the charged particle beam to theimage-shift operational coordinates.
 10. A charged particle beamapparatus according to claim 8, wherein: said display device includesdevice for inputting and displaying the selected converted coordinates,and said charged particle beam apparatus further comprises device forshifting the charge particle beam to an arbitrary position on theselected converted coordinates by directly inputting coordinates.
 11. Acharged particle beam apparatus according to claim 1, wherein saiddisplay device includes: device for inputting a pitch for the circuitline pattern, and counter device for displaying an integer part of aratio of the image-shift moving amount to the pitch.
 12. A chargedparticle beam apparatus according to claim 11, further comprising:device for inputting a count value to said counter device; and devicefor displaying a message on said display device when the integer part ofthe ratio of the image-shift moving amount to the pitch reaches aninputted count value.
 13. A charged particle beam apparatus according toclaim 1, further comprising: a charged particle beam source for emittinga charged particle beam; a condenser lens for focusing the chargedparticle beam; an objective lens for focusing the focused chargedparticle beam on the surface of the specimen; a deflector for scanningthe charged particle beam on the specimen; two image-shift deflectors;an optical axis control deflector; and device for adjusting deflectionsignals applied to said two image-shift deflectors independently of eachother or adjusting the ratio of one deflection signal to the other tomove the spot on the specimen irradiated with the charged particle beam,and adjusting a deflection signal applied to said one optical axiscontrol deflector to deflect a center axis of the charged particle beam,i.e., an optical axis to realize an objective lens axis which is capableof effectively eliminating chromatic aberration produced when thecharged particle beam is directed obliquely into said objective lens bysaid image-shift deflectors, and chromatic aberration produced by theimage-shift deflection.
 14. A charged particle beam apparatus accordingto claim 13, further comprising: device for superimposing the deflectionsignal applied to said one optical axis control deflector on thedeflection signal applied to the upper or the lower one of said twoimage-shift deflectors.
 15. A charged particle beam apparatus accordingto claim 13, wherein: said optical axis control deflector comprises twooptical axis control deflectors, and said charged particle beamapparatus further comprises device for adjusting deflection signalsapplied to said two optical axis control deflectors independently ofeach other or adjusting the ratio of one deflection signal to the otherto fix the object point of said objective lens.
 16. A charged particlebeam apparatus according to claim 15, further comprising: device forsuperimposing the deflection signals applied to said two optical axiscontrol deflectors on said two image-shift deflectors.